Presently, in order to meet exhaust gas regulations on a passenger diesel engine, a diesel oxidation catalyst (DOC), a diesel particulate filter (DPF), a lean NOx trap (LNT), and a selective catalytic reduction (SCR) unit are taken into account.
A post processing system mounted for reduction of the exhaust gas, such as the DOC, LNT, and SCR unit, requires a base temperature for chemical reaction.
In general, in a cold engine state (coolant temperature below 90° C.), when an exhaust gas temperature is low, excessive exhaust emissions are exhausted before the post processing system is activated. Consequently, an exhaust gas temperature increasing strategy is used for reducing the cold state exhaust gas even though fuel consumption is sacrificed.
However, although raising the exhaust gas temperature is possible by using a burning strategy, since intake air is discharged without a burning process, resulting in cooling down of the post processing system in a case of the overrun (coasting, or an imperfect combustion state), the temperature of the post processing system is lowered, delaying a time period for reaching the activation temperature.
The above information disclosed in this Background section is only for enhancement of understanding of the background of the invention and therefore it may contain information that does not form the prior art that is already known in this country to a person of ordinary skill in the art.